1. Field of the Invention
This invention relates generally to the reclamation of coking wastes.
More specifically, this invention relates to the treatment of tar decanter sludges, wash oil muck and like wastes to produce an oil fraction suitable in use as a fuel oil and a coke breeze fraction having high fuel value.
A preferred embodiment of this invention utilizes a reclaimed rolling oil as a treating agent in the process.
2. Description of the Prior Art
The coking of coal produces a variety of volatile products. These volatile products of carbonization comprise a mixture of permanent gases; condensible vapors of water, ammonia and various organic compounds including benzene, toluene, naphtalene and related compounds; and finely divided liquid and solid droplets or particles of tar and coke breeze. Coal tar and much of the coke breeze are separated from the coke oven off-gas by cooling in condensers. The residual cooled gases pass through a series of subsequent scrubbing steps including a light oil recovery stage.
Condensed coal tar, comprising a mixture of tar, water and coke breeze, is typically passed to a decanter from which a coal tar fraction is separated. The decanting step also produces a waste fraction, known as tar decanter waste or sludge which typically contains some 30 to 60% by weight of coke breeze solids and varying amounts of water in addition to coal tar. The tar decanter waste is a very viscous material, difficult to pump and inconvenient to handle as a solid. It is usually considered a useless waste material disposed of by land filling although some attempts have been made to recycle it to the coal charge supplied to the coking ovens.
Light oils are commonly removed from cooled coke oven off-gases by absorption in a suitable wash oil which is usually a petroleum distillate boiling above about 250.degree. C. The light oil which comprises aromatic compounds including benzene, toluene, xylenes and naphthalene, is stripped from the wash oil by distillation and the wash oil is cooled and then recirculated to the gas scrubbers. Another waste product, known as wash oil muck, is produced during this process.
The wash oil muck is a semi-liquid having the appearance and flow characteristics of a black mayonnaise. Its composition includes wash oil, light oil, finely divided coke breeze and water. Like tar decanter sludge, the wash oil muck if generally considered a worthless by-product usually disposed of by land filling. Both products, of course, have considerable fuel value but neither can be utilized in conventional fuel burning devices.
A coal tar is also produced during the gasification of coal as in the Lurgi process. It is known, as is taught by the Benade Pat., U.S. Pat. No. 3,992,281, to separate such tar from solid contaminants comprising chiefly coal dust and ash. Benade accomplishes this result by mixing with the residual tar a light oil, presumably aromatic, derived from the processing of that same tar. Light oil and tar residue are mixed together by flow through a pipe and then passed to a gravity separator. A clear, dissolved tar is drawn off the top of the separator while settled solids and water are drawn off the bottom.